A motor vehicle electric power steering generally comprises an electromechanical actuator situated on the steering column or on the lower assembly which comprises mechanical components intended to perform the angular positioning of the steered wheels of the vehicle. The electromechanical actuator comprises a rotary electric motor the shaft of which is supported by at least one rolling bearing, either directly or via a ball-screw system.
The rolling bearing generally comprises an inner ring, an outer ring and a row of rolling elements, generally balls, arranged between the rings.
A retaining cage for a rolling bearing comprising a plurality of pockets for housing balls each of which is defined in part by two claws arranged on the opposite side to a heal of the cage is known from document FR-A1-2 911 934. Such cages are completely satisfactory in a great many applications. However, in applications involving a low rotational speed, or in applications in which the direction of rotation reverses sharply, this kind of cage runs into various difficulties. Specifically, under the effects of the balls, the cage may suffer extensive deformation and come into contact with the inner ring, causing it to become damaged or even destroyed.
In addition, when the direction in which the load is applied to the bearings changes, for example when the wheels of a vehicle equipped with an electric power steering as described above are turned as the driver manoeuvres to the left and to the right when parking the vehicle, the cage is likewise severely deformed, or even destroyed. Moreover, it may prove difficult to fit such a cage over the balls.
A cage for a rolling bearing and comprising first pockets for the balls provided with axial retention claws for retaining the cage on the balls, and second pockets not provided with axial retention claws and dimensioned so that the associated balls are offered a relatively large degree of play so that they can move radially and circumferentially with respect to the second pockets is also known, from document FR-A1-2 883 941.
With such a cage, the interaction between the balls housed in the second pockets and the cage is reduced. In addition, the balls are able to move relative to one another, limiting the risk of deformation in the event of antagonistic movements of two adjacent balls. Moreover, it is easier to fit the cage over the balls in so far as only part of the pockets is equipped with the axial retention claws.
However, clipping the claws onto the balls when fitting the cage may cause small cracks to appear on the cage, and this may cause more rapid deterioration in service.
One aim of the present invention is to overcome these drawbacks.
More particularly, the present invention seeks to provide a cage for a rolling bearing that is easy to fit and that offers good reliability.
The present invention also seeks to provide a cage of small size, limited weight and which is not very deformable in service.
In one embodiment, the rolling bearing cage intended to provide the circumferential spacing of a row of rolling elements comprises first pockets for first rolling elements of the row, these pockets being provided with axial retention means for retaining the cage on the rolling elements, second pockets for second rolling elements of the row and not provided with axial retention means for retaining the cage on the rolling elements, and separation portions which between them delimit first and second pockets. Each separation portion delimiting one of the first pockets comprises a notch which is open axially and opens radially onto each side of the separation portion.
Advantageously, the notch leaves remaining at the separation portion a tab connected to the wall of the associated first pocket.
In one embodiment, the notch is open axially on the opposite side to the pockets.
The cage may comprise an axial portion from which the separation portions project. The notches of the separation portions may be open axially in the direction of an end face of the axial portion which is on the opposite side to the axial retention means.
In one embodiment, the first pockets comprise a spherical wall of constant thickness.
Each separation portion delimiting one of the first pockets may comprise a claw extending circumferentially towards the claw of the adjacent separation portion and forming the axial retention means.
In one embodiment, the separation portions delimiting the second pockets each comprise a cavity open axially on the opposite side to the pockets and radially towards the inside. Alternatively, or as a combination, the separation portions each comprise a cavity open axially on the opposite side to the pockets and radially towards the outside.
In another embodiment, each separation portion delimiting one of the second pockets comprises a cavity open axially on the opposite side to the pockets and opening radially on each side of the separation portion.
Each separation portion delimiting one of the second pockets may comprise a notch open axially on the same side as the pockets and opening radially on each side of the separation portion. The second pockets may have substantially cylindrical lateral walls.
The cage may, for example, be made as a single piece in a synthetic material, preferably, in a polymer material.
A second aspect of the invention relates to a rolling bearing comprising an outer ring, an inner ring, at least one row of rolling elements which are arranged between the rings, and a cage as defined hereinabove.
A third aspect of the invention relates to a motor vehicle electric power steering comprising at least one rolling bearing as defined hereinabove.